Method of fabricating a fuel rod having a porous plug

ABSTRACT

Method of manufacturing a fuel rod having a jacket and a porous plug by forming a laminate, the layers of which have porous passages between them, cutting a plug for the fuel rod from the laminate so that some of the passages between the laminated layers are included in the plug, whereby a porous plug is obtained, and welding the resultant plug to the fuel rod jacket.

United States Patent Van Dievoet 5] Oct. 24, 1972 [54] METHOD OF FABRICATING A FUEL ROD HAVING A POROUS PLUG [72] Inventor: Jean-Paul Laurent Van Dievoet, Bruxelles, Belgium [73] Assignee: Societe Beige pour llndustrie Nucleaire, S.A.Belgonucleaire, Bruxelles, Belgium [22] Filed: Nov. 24, 1969 [21] Appl. No; 879,128

[30] Foreign Application Priority Data Nov. 29, 1968 Belgium ..724.655

[52] US. Cl ..29/458, 29/400 N, 29/474.3, 176/79 [51] Int. Cl ..B23p 3/00, B23p 25/00 [58] Field of Search.176/79; 29/420.5, 400 N, 474.3, 29/458, 527.2

[56] References Cited UNITED STATES PATENTS 3,367,021 2/1968 Beghi et a1. ..l76/79 X 3,087,879 4/1963 Walker et al. ..176/79 3,324,540 6/ 1967 Lotts et al ..29/420.5 3,478,412 1 1/1969 Perona et al ..29/474.3 X

Primary Examiner-John F. Campbell Assistant Examiner-D. C. Reiley Attorney-William D. Hall, Elliott I. Pollock, Fred C. Philpitt, George Vande Sande, Charles F. Steininger and Robert R. Priddy [57] ABSTRACT Method of manufacturing a fuel rod having a jacket and a porous plug by forming a laminate, the layers of which have porous passages between them, cutting a plug for the fuel rod from the laminate so that some of the passages between the laminated layers are included in the plug, whereby a porous plug is obtained, and welding the resultant plug to the fuel rod jacket.

3 Claims, 4 Drawing Figures METHOD OF FABRICATING A FUEL ROD HAVING A POROUS PLUG The present invention relates to fuel rods for nuclear reactors and more particularly to fuel rods used within fast neutrons reactors.

As the combustion rate within fast reactors is very high, the rods are subjected during their irradiation inside of the reactor, to a constantly increasing pressure as a result of the build-up of fission gases, which causes a swelling of these rods and creates thus a supplementary loss of pressure for the coolant flowing alongside the rods.

In order to reduce the pressure of the gas, it is known to extend the rods by a holder, the volume of which fixes the value of the maximum pressure. This tank causes a very important supplementary loss of pressure.

In order to provide vented rods, it has been proposed to use porous jackets for the fuel, which lead to unsatisfactory results due to the difficulty of reaching the desired porosity. As a matter of fact, such a jacket must be selective and must allow the passage of fission gases while avoiding the passage of other vapors which may be formed inside or outside of the jacket and which risk to block up the porous wall. Moreover, the jacket must keep very good mechanical properties, a property which is hardly compatible with the porosity.

Another proposed solution is to make porous the welding of the plug with the jacket; this solution must also be eliminated as the proposed weldings may no more insure the necessary mechanical resistance.

The present invention relates to a porous plug which may be welded on the jacket and affords a selective porosity for the fission gases.

The method of manufacturing the porous plug according to the invention is characterized in that the plug is cut out of a sectional metallic-based material containing impurities having undergone a preferential orientation of the metallic crystals by means of a plastic deformation.

This crystal orientation of metallic sectional irons may be obtained by different operations well known by the men skilled in the art, as, for instance, successive drawing, laminating, extrusion or a combination of these operations.

Such a plug, as a result of its important mass compared to the jacket, has a sufficient mechanical resistance in spite of its porosity.

By cutting plugs of suitable shapes out of the treated materials, plugs having a metallurgic structure with a line-up orientation of the crystals can be obtained. This structure confers to the plug a selective porosity which is very convenient for the release of fission gases, while the greatest part of the vapors and other products may be stopped by interposition of a conventional filter placed between the fuel and the plug of metallurgic porosity.

It is obvious that, according to the method of the invention, plugs can be manufactured with porous passages in different directions, according to the transversal or longitudinal direction of the cutting out of the laminated piece.

The invention will be described with more details with the help of non limitative examples which are given hereafter with reference to the enclosed drawings which represent:

FIG. 1 a perspective view of a drawn rod;

FIG. 2 a schematic section of the extremity of a rod provided with a plug cut out of the rod represented on FIG. 1;

FIG. 3 a perspective view of a thick laminated sheet-iron with a transversal outcut;

FIG. 4 a schematic section of the extremity of a fuel rod provided with a plug cut out of the sheet-iron of FIG. 3.

Referring to FIG. 1, it shows a perspective view of a drawn rod partly split which will be cut into slices forming plugs. As the crystals will be oriented in the direction of the axis, it is possible to obtain discs with porous passages in this direction. The rod of the FIG. 2 is composed of a jacket 1 filled up with fuel pellets 2 and provided with a plug 3 fixed on the jacket 1 by the welding 4. The plug, made of a disc cut out of the rod shown on FIG. 1, will have porous passages represented by the arrows 5, through which the fission gases may be released. The reference number 6 represents a classical filter.

FIG. 3 shows a representative view partly split from a thick laminated sheet-iron which may be cut out as it is shown by the outcut 7.

The rod of FIG. 4 includes the same elements as FIG. 2 but the plug is made of the cut out piece 7 shown on FIG. 3.

The rod shown on FIG. 1 and the sheet-iron shown FIG. 3 may be manufactured by any known means, either using metallic powders or spongy metals, or by winding or superposing thin sheet-metals oxidized on their surface.

The oxidation may be carried out for instance by a thermal treatment in an oxidizing atmosphere and the degree of porosity may then be regulated by the duration of the treatment or by the temperature.

An example of the manufacturing of a rod according to FIG. 1 is described hereafter in a non restrictive way Elementary metallic powders, principally iron, nickel and chromium, having grain diameters between 40 and microns, are mixed up and compacted using a feeble pressure of about 1.5t/cm in order to form a block of stainless steel. This block will then be enclosed in a protective envelop which will protect it from oxidation during ulterior handling. This block will be afterwards converted into a rod by drawing, this operation being realized using a reduction ratio of 3.

The resulting rod is then cut into slices which constitute the porous plugs. These plugs, being tested, have shown a good porosity for xenon and krypton which are the principal elements of fission gases released during the irradiation of nuclear fuel.

The advantages of the proposed porous plugs are obvious and may be summarized as follows 1. Reduction of the sizes of fuel rods; as a matter of fact, it will no more be necessary to introduce a holder for the accumulation of fission gases, its absence leading to a reduction of the loss of pressure of the coolant which circulates alongside these rods and, consequently, to a greater output of energy.

2. There are less problems of swelling of fuel rods by the fission gases.

3. In the case of gas cooled fast reactors, the plug enables the balance of the pressures outside and inside of the rod.

It is clear that the invention is in no way limited to the methods of execution described hereabove. Thus, for instance, one may cut out the plug using a material which has been treated in another way. It is obvious that the plug may be also cut out of the sheet-metal shown on FIG. 3, cutting whether in a parallel direction or in a perpendicular direction to the laminating process or in the plane of the latter. Other means of orientation of the crystals, well known by the men skilled in the art, may be used.

I claim:

1. Method of manufacturing a fuel rod having a jacket of the assembly and a porous plug, said method comprising superposing thin sheets of metal to form a layered assembly, pressing together layers of the assembly to form a laminate in which the layers are bonded together with directionally oriented porosities between said layers, cutting a plug for said fuel rod from said laminate said plug containing some of the porosities of the laminate, whereby a porous plug is obtained, and welding the resultant plug to the fuel rod jacket.

2. Method of manufacturing according to claim 1 wherein said layers are formed of metallic-based refractory material containing impurities, said material having been subjected to plastic deformation for introducing preferential orientation into its metallic crystalline structure.

3. Method of manufacturing according to claim 1 wherein said layers are coated with metallic oxide.

P0405) I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 699,638 Dated October 24, 1972 I Jean-Paul L. Van Dievpet It is certified that error appears 'in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1, line. 2 please delete of the assembly Signed and sealed this 13th day of March 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner'of Patents Po-ww UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- ,6 8 Dated October 24, 19 72 Inventor(5) Jean-Paul L. Van Di evoet It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1, line 2 please delete of the assembly Signed and sealed this 13th day of March 1973.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. ROBERT GOTT SCHALK Attesting Officer I Commissioner of Patents 

1. Method of manufacturing a fuel rod having a jacket of the assembly and a porous plug, said method comprising superposing thin sheets of metal to form a layered assembly, pressing together layers of the assembly to form a laminate in which the layers are bonded together with directionally oriented porosities between said layers, cutting a plug for said fuel rod from said laminate said plug containing some of the porosities of the laminate, whereby a porous plug is obtained, and welding the resultant plug to the fuel rod jacket.
 2. Method of manufacturing according to claim 1 wherein said layers are formed of metallic-based refractory material containing impurities, said material having been subjected to plastic deformation for introducing preferential orientation into its metallic crystalline structure.
 3. Method of manufacturing according to claim 1 wherein said layers are coated with metallic oxide. 